1. Field of the Invention
The present invention relates to a liquid developing method and a liquid developing device for developing an electrostatic latent image formed on a latent image carrying member via a toner dispersed in a carrier liquid.
2. Description of the Related Art
Electrophotographic methods for image formation, wherein an electrostatic latent image formed on a latent image carrying member such as a photosensitive member or the like is developed by a charged toner, can be broadly divided into dry developing methods which directly employ a toner powder, and liquid developing methods which employ a liquid developer having a toner dispersed in a carrier liquid.
The liquid developing method was invented in 1955 by Mr. Metcalfe, a resident of Australia. In general, an electrostatic latent image formed on the surface of a photosensitive member is developed by immersing the photosensitive surface in a liquid developer. Typically, in liquid developing methods, images are obtainable which have high resolution and excellent halftones because toners having a small particle diameter are used. Moreover, toner images of such methods are advantageous inasmuch as they are easily fixed to a transfer member.
In recent years, demand has increased for images with more detail, and toner particles have been made even smaller in response to the demand. However, the mean particle diameter of toner is about 6 .mu.m in dry developing methods. In contrast, the mean particle diameter is on the submicron level in liquid developing methods because the toner is dispersed in a liquid medium. Thus, liquid developing methods are advantageous in that they produce higher image quality.
In liquid developing devices which develop by liquid developing methods, toner is mechanically adhered to the photosensitive surface when liquid developer comes into contact with the photosensitive surface because the toner is dispersed in the liquid developer. This situation is the cause of background fogging.
For example, GB 1250214 proposes developing an electrostatic latent image by separating toner on an insulated belt immersed in a liquid developer, and having the thus formed toner layer transferred to an opposite surface.
However, all the conventional methods employ a developer layer (toner layer) directly in contact with a photosensitive surface thereby preventing the elimination of background fogging. Furthermore, toner temporarily adhered to a photosensitive surface becomes stressed when interposed between the photosensitive surface and the surface of a developing roller, thereby causing image disturbance.